From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:36083) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cj3mR-0007iO-46 for qemu-devel@nongnu.org; Wed, 01 Mar 2017 07:54:56 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cj3mO-0001nR-2h for qemu-devel@nongnu.org; Wed, 01 Mar 2017 07:54:55 -0500 Received: from mx1.redhat.com ([209.132.183.28]:17201) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1cj3mN-0001nL-TC for qemu-devel@nongnu.org; Wed, 01 Mar 2017 07:54:52 -0500 Date: Wed, 1 Mar 2017 14:54:49 +0200 From: "Michael S. Tsirkin" Message-ID: <20170301145306-mutt-send-email-mst@kernel.org> References: <20170301115004.96073-1-pasic@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170301115004.96073-1-pasic@linux.vnet.ibm.com> Subject: Re: [Qemu-devel] [PATCH 1/1] virtio: fallback from irqfd to non-irqfd notify List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Halil Pasic Cc: qemu-devel@nongnu.org, Paolo Bonzini , Stefan Hajnoczi , Cornelia Huck On Wed, Mar 01, 2017 at 12:50:04PM +0100, Halil Pasic wrote: > The commits 03de2f527 "virtio-blk: do not use vring in dataplane" and > 9ffe337c08 "virtio-blk: always use dataplane path if ioeventfd is active" > changed how notifications are done for virtio-blk substantially. Due to a > race condition interrupts are lost when irqfd is torn down after > notify_guest_bh was scheduled but before it actually runs. Furthermore > virtio_notify_irqfd ignores the value returned by event_notifier_set > which correctly indicates that notification has failed due to bad file > descriptor. > > Let's fix this by making virtio_notify_irqfd fall back to the non-irqfd > notification mechanism if event_notifier_set fails. > > Signed-off-by: Halil Pasic > --- > > This is probably not the only way to fix this: suggestions welcome. I > did not use a fixes tag because I'm not sure yet where exactly things got > broken. Maybe guys more familiar with dataplane an coroutines can help > (Paolo, Stefan). > --- > hw/virtio/virtio.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c > index 23483c7..8e1c1e9 100644 > --- a/hw/virtio/virtio.c > +++ b/hw/virtio/virtio.c > @@ -1581,7 +1581,9 @@ void virtio_notify_irqfd(VirtIODevice *vdev, VirtQueue *vq) > * to an atomic operation. > */ > virtio_set_isr(vq->vdev, 0x1); > - event_notifier_set(&vq->guest_notifier); > + if (event_notifier_set(&vq->guest_notifier)) { > + virtio_notify_vector(vdev, vq->vector); > + } Does this fail because the underlying fd got closed? Then there's a problem: trying to write to a closed fd might corrupt an unrelated fd. If you want to use this way we need to set fds to -1 when we close. > } > > static void virtio_irq(VirtQueue *vq) > -- > 2.8.4